A number of technologies exist for the short range communication of information between mobile devices. These technologies include infra-red based technologies and low-power radio technologies (including, in particular, the recent “Bluetooth” short range wireless standard). Depending on the technology implementation, differing types of message propagation will be enabled including asynchronous message broadcast, and multicast and point-to-point duplex connections established after coordination and negotiation between communicating devices.
One possible use for such short-range technologies is the transmission of local information to passers-by equipped with mobile devices having short-range transceivers, the local information being, for example, transmitted by a shop to inform the passers-by of current promotions. Another use is in location beacons that transmit location information to passers-by.
It is known, for example from EP-A-0,948,222, to diffuse information amongst users by short range wireless links so that a user need not be in range of an originating transmitter in order to receive the information sent out by the latter. Such an arrangement is likely to be particularly useful in environments such as shopping malls, city centers, tourist attractions, theme parks or any other location where large numbers of users carrying mobile devices with short-range transceivers are likely to be in one locality. Another important area of application is the diffusion of information between devices fixed in cars.
FIG. 1 of the accompanying drawings depicts an information diffusion process in which an originating information point 10 (typically fixed, but not necessarily so) sends out the information over a short-range radio link to nearby mobile devices, in this case device 11. The receiving device 11 transmits on the information to a neighboring device 12 and then moves (see dashed arrow in FIG. 1) before sending on the information again to another device 14. Meanwhile mobile device 12 has moved into proximity with device 13 to which it also transmit the information. Device 13 now moves near to the device 14 and passes the latter the information—however, as device 14 already has the information from device 11, it ignores the copy from device 13. Device 13 also passes the information to a fixed relay transceiver which subsequently passes the information to a mobile device 15. Finally, device 15 passes the information to device 14 which has now within range of device 15; again, device 14 ignores the copy information from device 15.
It can be seen that information can be rapidly diffused among the population of mobile-device users in the general vicinity of the source 10. So, the process of diffusion takes advantage of both the short range wireless technology and the movement of the users carrying the devices.
By applying appropriate diffusion-limiting mechanisms (for example, by assigning the original information a total time to live of, for example, 10 minutes), the information will generally only be diffused in the vicinity of the originating point 10. This makes the diffusion process appropriate for the diffusion of location relevant information that is primarily of use only in the vicinity of point 10.
The advantages of using short-range diffusion over sending data on a cellular network such as GSM, are avoidance of the cellular charges, and the availability of much higher bit rates.
The diffused information can, of course, include the location of the originating point. For devices receiving the information directly from the originating point, this provides them with a fairly accurate indication of their location (because the information is received over a short-range link). However, as the information is diffused between devices, the newly-receiving devices get less and less accurate location information.
It is an object of the present invention to provide a location discovery means using the diffusion of location information that is more general in application.